The present invention relates to control apparatus for controlling luminescence provided by a light source and to lighting apparatus comprising the control apparatus.
In the past designers attempted to provide lighting apparatus which mimics a candle and which can be used to provide light similar to that of a naked flame. The problem faced by designers is to provide realism.
In DE-A-2729466 there is described lighting apparatus which uses a single lamp to simulate a single candle or a group of individual lamps to simulate a group of individual candles. The luminosity of each lamp is controlled using electronically generated signals driving Triac power switching of the mains electric supply. Each lamp is given an "address" so that each lamp can be individually controlled with different electronic signals (sixteen lamps are proposed). The electronic signals are synthesized from individual generated signals which represent four different levels of luminosity (one of which is a zero level) and six different frequencies of switching between these levels. The frequencies and levels are combined electronically to give six characteristic control signals which can be applied to each addressed lamp (i.e. six signals which have a set frequency and amplitude of lamp luminosity). These are divided into two groups, one for quiet air conditions and one for conditions where there is a strong draft.
The six characteristic control signals of DE-A2729466 are derived from observation of the behavior of a single real candle flame, its behavior in a group of mounted candles and when subjected to a draft of air.
DE-A-2729466 proposes that the six signals are adequate to give a reasonable simulation of a candle flame when switched to individual lamps in a pseudo-random manner.
To take into account the effect of a draft of air, a wind sensor in the form of a temperature sensitive resistor is used to detect the air movement which responds by triggering the selection of the first or second group of signals. It follows that the behavior of the lamp luminosity will follow a predictable sequence when the wind sensor detects quiet conditions. In a group of lamps, individual lamps will be responding to different parts of the sequence at any given moment. If the wind sensor detects a strong enough air movement to trigger the circuits into the fast frequency mode then the luminosity changes will be controlled by the second group of signals.
DE-A-2729466 proposes a solution to the problem of providing a candle flame look-alike with minimal fire risk, for use, typically, as a visual prop on a theatre stage. While the control programme for controlling operation of the lamp in DE-A-2729466 is selected having regard to a wind sensor output signal, once an operating mode (e.g. a fast frequency mode) is selected the control of the lamp is carried out in that mode independent of variations in sensed wind speed until the wind speed changes to such an extent that a different mode of operation (e.g. a slow frequency mode)is selected. When a mode of operation is selected then there will be variations in the luminescence of the lamps without any change in wind speed, but purely due to the preprogrammed signals.
The present invention provides a control apparatus for controlling luminescence provided by a light source which comprises sensor means for sensing motion of air and means for varying the luminescence provided by the light source when motion of air is sensed, characterized in that the sensor means is an air pressure sensor and all changes in the luminescence provided by the light source are occasioned by sensed changes in air pressure.
The significant different between the present invention and the systems of the prior art starts with the perceived problem to be solved. Prior art systems such as are described in DE-A-2729466 and U.S. Pat. No. 4,593,232 are primarily directed at producing a device which looks like a candle when lit and which is intended as an item of display. The present invention is aimed at producing a light source which when used to control a light source in a room or defined space produces lighting conditions which mimic those of a real candle, and as far as possible an apparatus that looks and behaves like a real candle. To this end, the luminance levels produced by the present system must be adequate (e.g. the light source must be an effective light source which consumes 20 to 100 watts of power, rather than a purely decorative light source) and the response of the lighting apparatus to its environment must closely approach that of the real candle.
The most significant response of a candle flame to its environment is the way in which the candle flame follows changes in the local air movements and pressure changes. (These can be respectively considered akin to electrical current and voltage). Since air movements create pressure changes, the concept developed for the present invention is to sense environmental pressure changes using a pressure sensor such as a microphone to generate control signals and to adjust the bandwidth of the control signals to produce a visual effect on a room illumination which simulates candle flame. The pressure sensor is the only source of the signals that control the light source and all changes in luminescence are due to changes in air pressure rather than a preprogrammed routine of variation with time.
Both U.S. Pat. No. 4,594,343 and DE-A-2729466 lack the concept of simulation and concentrate on electronically generating signals which cause the lamps to change intensity and flicker in an apparently random manner generally regardless of the space environment of the device. Although the system of DE-A-2729466 recognises an air stream which is significantly noticeable as a draft as influencing the simulated flame, the sensor is only used to switch in a more vigorous programme of lamp brightness control and does not attempt any apparent physical movement simulation.
Preferably, the light source to be controlled is an electric lamp and the means for varying the luminescence of the light source comprises means for controlling current supplied to or voltage applied across the electric lamp.
Preferably the light source to be controlled comprises a plurality of electric lamps, and the means for varying the luminescence of the light source comprises means for controlling current supplied to or voltage applied across each of the electric lamps. Preferably, each electric lamp is supplied with a periodic electrical waveform and the means for varying the luminescence of the light source varies the luminescence by synchronised switching during the period of the periodic electrical waveform. Preferably, the control apparatus introduces a phase difference in the synchronous switching of first periodic electrical waveform supplied to a first electric lamp and a second periodic electrical waveform supplied to a second electric lamp.
In U.S. Pat. No. 4,593,232 it is recognized that movement is an important characteristic of candle flame that must be simulated, hence a multi-filament lamp is used with the current/voltage applied to each filament being varied independently of the others to achieve a simulated motion. However, the control program for the lamp is entirely synthetic and ignores totally the environment. The two filaments do not have a mutually dependent `flicker` control signal and hence the apparent flame movement will again be pseudo-random, but independently so (i.e. the flicker will not change with variations in air pressure).
Observation of a real candle flame shows that provided there is no restriction of air flow to the candle, the apparent average total luminescent power emanating from the candle varies very little with most air pressure changes and movement, unless of course it is strong enough to blow the candle out. However, because the candle flame has almost negligible mass, it will respond by physical movement to quite high frequency changes of air pressure extending as far as the lower end of the audio frequency range. It is this responsiveness which provides much of the `flicker` effect of a candle.
The concept of using two or more filaments to achieve apparent movement of illumination is a logical step once the intellectual step has been taken to recognize that the movement of the light source is an important requirement of the simulation. However, it does not follow that a simple recognition of the need for the light source to apparently move, will logically lead to the conclusion that the movement should be controlled by means of sensing the air pressure over a fairly wide bandwidth of frequencies. Instead, a second intellectual step is required to recognise that control using an air pressure based signal will contain all the components of movement that are required, including the higher frequency `flicker` effects that the prior art systems have created either by elaborate synthesis or inadequate ON/OFF switching.
It also follows that the dual lamp arrangement has to use lamps with filaments which are small and are responsive to the frequency of the control signals applied. A superior performance in this respect is given by the use of Halogen lamps.
Rather surprisingly, the fuller simulation of the present invention provided by use of an air pressure sensor is technically easier to achieve than the synthesis of control signals used in the prior art systems.
The present invention is different in that the simulated candle functions by responding to those air conditions which a real candle, placed in the same position, would also respond to at any given time. It produces a level of illumination which can be adjusted to match that of a candle and will illuminate a room with changing light patterns in a very similar way to a real lighted candle. It is to be expected that such a device will look as if it is behaving like a candle if sensibly constructed. In fact it is possible to stand the real and the simulated candle side by side and watch the rather uncanny similarity of behavior.
An embodiment comprising a plurality of electric lamps can comprise a plurality of pairs of electric lamps, the lamps of each pair being located adjacent to each other, wherein a first electric lamp of each pair is supplied with the first periodic electrical waveform and a second electric lamp of each pair is supplied with the second periodic electrical waveform.
Where in the specification and claims reference is made to a light source comprising a plurality of electric lamps, this should be construed as including:
1. arrangements in which separate electric bulbs are provided each with its own single filament; PA0 2. arrangements in which a plurality of independent filaments are provided in one single bulb; and PA0 3. arrangements in which a plurality of separate electric bulbs are provided each with a plurality of filaments.